Localized alloying for improved bond reliability

Abstract

Methods of forming gold-aluminum electrical interconnects are described. The method may include interposing a diffusion retardant layer between the gold and the aluminum, the diffusion retardant layer including regions containing and regions substantially devoid of a diffusion retardant material; bringing into contact the diffusion retardant layer, the gold, and the aluminum; forming alloys of gold and the diffusion retardant material in regions containing the material and forming gold-aluminum intermetallic compounds in regions substantially devoid of the material; and forming a continuous electrically conducting path between the aluminum and the gold. A structure for gold-aluminum interconnect is provided. The structure may include an aluminum alloy bond pad and a diffusion retardant layer in contact with the bond pad, the diffusion retardant layer including regions containing and regions substantially devoid of a diffusion retardant material. The structure may include a gold free air ball in contact with the diffusion retardant layer.

The invention claimed is: 
     
       1. A structure suitable for use in a gold-aluminum interconnect, the structure comprising:
 an aluminum alloy bond pad; 
 a diffusion retardant layer in contact with the bond pad, the diffusion retardant layer comprising regions containing a diffusion retardant material and regions substantially devoid of the diffusion retardant material; and 
 a gold ball bond in electrically conductive bond forming contact with both the diffusion retardant material and portions of the bond pad exposed therethrough. 
 
     
     
       2. The structure of  claim 1 , wherein:
 the diffusion retardant material comprises one or more of copper, molybdenum, rhodium, palladium, silver, rhenium, iridium, and platinum. 
 
     
     
       3. The structure of  claim 1 , wherein the diffusion retardant layer is interposed between the gold ball bond and the aluminum alloy bond pad. 
     
     
       4. The structure of  claim 3 , wherein:
 the gold has an interdiffusion rate into the diffusion retardant material less than an interdiffusion rate of the gold into the aluminum. 
 
     
     
       5. The structure of  claim 3 , further comprising:
 an interfacial region comprising at least one phase of gold-aluminum intermetallic compounds in the regions substantially devoid of the diffusion retardant material, and at least one phase of gold alloyed with the diffusion retardant material in the regions containing the diffusion retardant material, wherein the regions substantially devoid of the diffusion retardant material are laterally distributed, throughout the interfacial region, amongst the regions containing the diffusion retardant material. 
 
     
     
       6. The structure of  claim 3 , further comprising:
 a gold wire in contact with the ball bond. 
 
     
     
       7. The structure of  claim 3 , wherein:
 the aluminum alloy bond pad comprises aluminum alloyed with copper; 
 the diffusion retardant material comprises palladium with trace impurities; 
 at least one gold-palladium alloy is formed in regions containing the palladium; and 
 at least one gold-aluminum intermetallic compounds is formed in regions substantially devoid of palladium; 
 and further comprising a continuous electrically conductive path between the bond pad and the ball bond. 
 
     
     
       8. A packaged integrated circuit comprising:
 a package substrate; 
 an integrated circuit; 
 an aluminum bond pad formed on the integrated circuit; 
 a gold ball bond; and 
 a diffusion retardant layer in direct bond forming contact with both the aluminum bond pad and the gold ball bond, the diffusion retardant layer comprising regions containing a diffusion retardant material and regions substantially devoid of the diffusion retardant material, wherein the electrically conductive bond forming contact includes an interfacial region comprising least one phase of gold-aluminum intermetallic compounds in the regions substantially devoid of the diffusion retardant material, and at least one phase of gold alloyed with the diffusion retardant material in the regions containing the diffusion retardant material. 
 
     
     
       9. The packaged integrated circuit of  claim 8 , wherein:
 the diffusion retardant material comprises one or more of copper, molybdenum, rhodium, palladium, silver, rhenium, iridium, and platinum. 
 
     
     
       10. The packaged integrated circuit of  claim 8 , wherein:
 the gold has an interdiffusion rate into the diffusion retardant material less than an interdiffusion rate of the gold into the aluminum. 
 
     
     
       11. The packaged integrated circuit of  claim 8 , further comprising:
 a gold stud bump in electrical contact with the aluminum bond pad. 
 
     
     
       12. A structure suitable for use in a gold-aluminum interconnect, the structure comprising:
 an aluminum alloy bond pad; 
 a diffusion retardant layer in contact with the bond pad, the diffusion retardant layer comprising regions containing a diffusion retardant material and regions substantially devoid of the diffusion retardant material; and 
 a gold ball bond in direct bond forming contact with both the diffusion retardant material and portions of the bond pad exposed therethrough. 
 
     
     
       13. The structure of  claim 12 , wherein:
 the diffusion retardant material comprises one or more of copper, molybdenum, rhodium, palladium, silver, rhenium, iridium, and platinum. 
 
     
     
       14. The structure of  claim 12 , wherein the diffusion retardant layer is interposed between the gold ball bond and the aluminum alloy bond pad. 
     
     
       15. The structure of  claim 14 , wherein:
 the gold has an interdiffusion rate into the diffusion retardant material less than an interdiffusion rate of the gold into the aluminum. 
 
     
     
       16. The structure of  claim 14 , further comprising:
 an interfacial region comprising at least one phase of gold-aluminum intermetallic compounds in the regions substantially devoid of the diffusion retardant material, and at least one phase of gold alloyed with the diffusion retardant material in the regions containing the diffusion retardant material, wherein the regions substantially devoid of the diffusion retardant material are laterally distributed, throughout the interfacial region, amongst the regions containing the diffusion retardant material. 
 
     
     
       17. The structure of  claim 14 , further comprising:
 a gold wire in contact with the ball bond. 
 
     
     
       18. The structure of  claim 14 , wherein:
 the aluminum alloy bond pad comprises aluminum alloyed with copper; 
 the diffusion retardant material comprises palladium with trace impurities; 
 at least one gold-palladium alloy is formed in regions containing the palladium; and 
 at least one gold-aluminum intermetallic compounds is formed in regions substantially devoid of palladium; 
 and further comprising a continuous electrically conductive path between the bond pad and the ball bond.